Cumulative Effects Assessment of Multiple Stressors on Coral Reef Health in the Gulf of Guinea

Coral reefs in tropical West Africa face simultaneous exposure to multiple anthropogenic and climatic stressors, yet quantitative cumulative effects assessments remain absent from the scientific literature for this region. This study assessed the cumulative effects of sea surface temperature anomalies, turbidity, nutrient enrichment, overfishing, and coastal development on coral reef health at six reef sites in the Gulf of Guinea off Nigerian and Cameroon waters. A cumulative effects assessment framework integrating spatial stressor mapping with biological response data was developed. Coral health was quantified through percentage live coral cover, coral colony size frequency distributions, coral juvenile density, and fish assemblage structure assessed during standardised SCUBA belt transect surveys. Remote sensing products were used to derive sea surface temperature, turbidity, and chlorophyll-a indices. A local stressor index was constructed from fishing pressure proxies and development intensity scores. Individual stressor-response relationships were characterised using generalised linear mixed models before cumulative effect calculation. Multiple regression revealed that cumulative stressor scores explained 74 percent of variance in live coral cover. The most severely impacted reefs experienced all five stressors at above-median intensity. Sites experiencing elevated sea surface temperatures combined with turbidity above 1.5 NTU showed synergistic negative interactions producing lower live coral cover than predicted by additive effects. Juvenile coral density was most strongly predicted by substrate availability and herbivore fish biomass. The study provides the first quantitative cumulative effects assessment for Gulf of Guinea reefs and identifies fishing pressure reduction as the most tractable management lever. Keywords: cumulative effects, coral reefs, Gulf of Guinea, multiple stressors, bleaching.